1. Field of the Invention
This invention relates to hydraulically assisted tubing expansion. In particular, but not exclusively, the invention relates to hydraulically assisted diametric expansion of tubing downhole.
2. Description of the Related Art
One of the most significant recent developments in the oil and gas exploration and production industry has been the introduction of technology which allows for expansion of extended sections of tubing downhole. The expandable tubing may take different forms, including but not limited to: casing, liner, sandscreen, straddles, packers and hangers. A variety of expansion methods have been proposed, including use of expansion cones or mandrels, which are forced through the tubing.
One difficulty that has been experienced with cone expansion is the requirement to apply significant forces to the cone to drive the cone through the tubing. The driving force may be applied mechanically, or hydraulically. Use of hydraulic pressure offers certain advantages, but typically requires the entire tubing to be pressurised, and also the provision of an effective seal or seals to prevent leakage of high-pressure fluid.
The sole use of fluid pressure to expand tubing, rather than mechanical expansion techniques utilising cones or other devices, is perceived to involve a degree of uncertainty, as it is difficult to predict how a particular tubular will expand in response to an internal fluid pressure which creates a force above the yield strength of the tubular. In particular, a point or area of relative weakness in the tubing wall may result in the tubing bursting or expanding in a non-uniform manner. In addition, and as noted above, use of elevated hydraulic pressure typically requires the entire tubing to be pressurised, and also the provision of an effective seal or seals to prevent leakage of high-pressure fluid.
A number of these difficulties are addressed in applicant's WO 02/081863, the disclosure of which is incorporated herein by reference, in which a tubing expansion process is described utilising a combination of both mechanical and hydraulic expansion forces. The use of a pulsed force in combination with a pulsed fluid pressure is disclosed in applicant's WO 02/103150, the disclosure of which is also incorporated herein by reference.
It is among the objectives of embodiments of the present invention to provide a method of expanding tubing, particularly in a downhole environment, which relies at least in part on hydraulic expansion forces.